Tunable magnetron of the resonator type



. July 22, 1947. R, B, NELSON TUNABLE MAGNETRON OF THE RESONATOR TYPE Filed Dec. 2, 1944 Inventor I Richard 5. Nelson,

by His Attorney. 4

,Illlllllllililil (II! iiillilltilll! Patented July 22, 1947 TUNABLE MAGNETRON OF THE RESONATOR TYPE Richard B. Nelson, Schenectady, N. Y., assignor' to General Electric Company, a corporation of New York Application December 2, 1944, SerialNo. 566,288

4 Claims.

My invention relates to electric discharge devices and more particularly to improved tuning arrangements for high frequency electric discharge devices of the magnetron type.

Numerous arrangements have been provided for tuning or adjusting the operating frequency 'ofmagnetrons of the type including a resonant anode structure in which a plurality of coupled resonant circuits are provided by openings through the'structure. For example, in Bondley application Serial No, 474,426, 'filedFebruary 2, 1943, and assigned to the assignee of the present invention there are described and claimed two tuning arrangements for magnetrons of this type in which movable elements are employed for varying the dielectric of the resonant circuits and thereby Varying the resonant frequency of the anode structure. In accordance with the present invention, I provide improved arrangements for tuning magnetrons and particularly tuning arrangements provided with means for varyingthe inductance of the resonant anode structure. In a preferred embodiment means are provided for simultaneously varying the inductance and capacitance of the resonant anode structure so that the ratio of L/C remains constant with adjustments in operating frequency. This "is particularly desirable in discharge devices of the magnetron type, as it tends to keep the coupling to the output circuit constant as the oscillator is tuned. This arrangement also tends to produce a morelinear variation in frequency with movement of the tuning structure, and gives. a greater tuning range than is conveniently obtainable by varying inductance or capacitance alone.

It is an object of my invention to provide .a new and improved electric discharge device.

It is another object of my invention to provide a new and improved tuning structure for a multi ple resonator electric discharge device.

.It is a still further object of my invention to provide a tuning arrangement for electric discharge devices of the magnetron type in which the variation in frequency is substantially linear with respect to displacement of the tuning struc- 'ture.

In one illustrated embodiment of my invention a resonant anode structure is provided with a plurality of circular openings which communicate with a central opening by means of gaps or slots. The anode sections interposed between the successive hole and slot combinations are conductively connected by straps so that alternate anode sections are maintained at one potential. A tuning ring mounted for movement toward and away from these conducting straps provides means for varying the effective capacity of the slots. A second conducting ring of larger diameter and in alinement with one endof the openings through the anode is moved toward and away from the anode structure to restrict "the flux through these openings and thereby to vary the effective inductance of the various openings of the anode structure. These two rings are coupled rigidly together and adjusted by a single operating mechanism so that the capacity and inductance are varied in the same direction as the structure is adjusted. In another embodiment of my invention a tuning member having the general shape ofan'internally threaded gear is'rotated with respect to the anode structure to cover more or less of the openings through the anode structure and in this way to control the inductance and the operating frequency of the device.

For a better understanding of my invention, reference maybe had to the following description taken in connection with the accompanying drawing in which Fig. l is an elevational View in sectionof a magnetron embodying my invention; Fig. '21s a sectional view, looking downwardly, on the line 2-'2 of Fig. l; Fig.3is a sectional view, looking upwardly, along the line 3-3 of Fig. 1; Fig. 4 is an elevational view in sectionof the modification of the tuning arrangement shown in Fig. 1, and Fig. 5 is a sectional view, looking downwardly, along the line 5-'5 of Fig. 4.

Referring now to Fig. 1 of the drawing, I hav'e shown my invention embodied in a tuning arshown) located communicates with the central opening by a slot or gap 5. In the particular embodiment illustrated, eight openings 3 and associated slots are provided, dividing the anode structure into eight similarly shaped anode sections 6. All the alternate anode sections are connected together on both faces of the anode structure by conducting straps 1 and 8. As clearly indicated in the drawing, the straps are located in the region of the slots or gaps 5. In order that the straps may present a plane surface, the anode sections are recessed in the region crossed by the straps. These recesses are clearly visible in Fig. 1 and are indicated by the numeral 9. Each strap is electrically connected to alternate anode sections, and insulated from the others by an increased depth of the recess 9.

A source of electrons within the opening 4 of the anode structure is provided by a suitable cathode structure which, as illustrated in Fig. 1. may be in the form of a cylindrical cathode sleeve in having end shields II for minimizing the escape of electrons from the interelectrode space. The cathode is supported from the cover of the envelope l by means of an elongated metal sleeve l2 which is secured to one end of the cathode and to a larger metal sleeve l3 which is supported from the cover of the envelope by an upstanding metal sleeve I 4 and a cylindrical insulating sleeve I5. The sleeve l2 may provide an externally accessible connection for a source of cathode voltage and has one terminal for a source of voltage for energizing a heater (not shown) within the cathode sleeve ID. The other connection for the heater is provided by a conductor l6 centrally supported within the supporting sleeve l2 and maintained in spaced relation thereto by insulators l1, only one of which is visible in the drawing. The sleeve [2 is joined to sleeve l3 by means of a cap IS. The end of the sleeve I2 is also sealed about conductor l6 by a, glass bead l9.

In accordance with an important feature of my invention, a tuning structure including an annular conducting plate 20, having inside and outside diameters chosen so that it will cover the symmetrically located openings 3 of the anode struotureyis arranged on one side of the anode structure and a smaller annular conducting member 2! is located on the opposite side of the anode structure and arranged to move toward and away from the conducting straps 1 and 8. In order that these tuning members or rings 20 and 2| may be moved in unison from the exterior of the envelope I, I provide rigid supporting members 22 which join the tuning rings 20 and 2| together and each of which extends to the exterior of the envelope l passing through a flexible metal bellows 23. The bellows 23 are open at the lower end and each is secured in a vacuum-tight relation to the envelope by a flange 24 which is welded to the end of the envelope. Threaded sleeves 25 surrounding the bellows and secured to the envelope receive threaded caps 26 which engage the upper ends of the bellows 23 and provide for the adjustment in position of the supporting rods 22 and as a result the position of the tuning rings 20 and 2 I.

As is well understood, the operation of magnetron devices of the character described above depends upon the existance of mutually perpendicular magnetic and electric fields in the interelectrode space. Therequlred magnetic field in a direction parallel to the axis of the cathode may be provided by a suitable electro-magnet (not on the exterior of the envelope and having pole pieces 21 and 28. High frequency energy may be coupled into or out of the resonant anode structure in any suitable manner. As illustrated in Figs. 2 and 3, a coupling loop 29 is located in one of the openings 3 and has one end secured to the wall of the opening. The other end extends from the envelope 1 as the central conductor 39 of a concentric type transmission line. The outer conductor 3| is sealed to the wall of the envelope I. It will be readily understood that an insulating vacuum seal, not shown, may extend across the transmission line.

As is well understood by those skilled in the art, the illustrated embodiment of my invention described above may operate as an oscillator to deliver high frequency oscillations to the output transmission line including conductors 3i) and 3!. When operating in this manner, electrons emitted by cathode I0 move in the interelectrode space between cathode l0 and the faces Of anode sections 6 to excite the resonant cavities comprising openings 3 and gaps 5. Resonant structures of this type including a. pluraltiy of coupled resonant circuits have a tendency to operate at any one of a number of modes or frequencies. Oscillation in the desired mode is enhanced by strapping or conductively connecting alternate anode sections so that alternate anode sections are at the same high frequency potential and adjacent anode sections are displaced electrical degrees at the frequency generated. With the tuning structure including rings 28 and 2| in a predetermined position, the pole and slot combinations have a definite capacity and inductance and tend to oscillate at a desired frequency. As the thumb caps 26 are adjusted to move disk 20 toward the anode structure and disk 2| away from the anode structure the inductance and the capacity are both reduced, thus increasing the frequency at which the structure resonates. Conversely, by adjusting the thumb caps 26 so that the plates 20 and 2| move upwardly, the inductance and capacity simultaneously increase. The conducting ring 20 prevents the passage therethrough of the high frequency electromagnetic flux which normally passes through the openings 3 and thus effectively reduces the inductive component of the resonant circuit, while the plate 2! varies the capacitive component. Simultaneous variation of inductance and capacity in addition to maintaining their ratio constant gives a more linear variation in operating frequency with movement of the tuning element. For this reason, the structure of the embodiment illustrated in Fig. 1 is particularly efiective.

In Figs. 4 and 5 are shown a modification of my invention in which tuning is accomplished by varying the effective magnitude of the inductive component of the anode circuits. The embodiment of Figs. 4 and 5 is similar in most respects to the embodiment of Fig. 1 and the same reference numerals have been employed to designate corresponding parts. In Fig. 4 the conducting straps 1 and -8 have been omitted. It will be understood, however, that these straps may be employed if desired. In the arrangement shown in Fig. 4 the anode structure 2 is provided with a transverse slot 32 which receives a circular tuning member 33 in the form of an annular disk having inwardly projecting tooth-like portions 34 which are arranged to be moved over variable portions of the openings 3 by rotation of the disk 33. As a means of moving the disk to elfect the adjustment in position of the disk 33,

'. an operating arm 35 joined to the ring 33 extends through a slot 36 in the side wall of the envelope I. As illustrated clearly in Fig. 5, the arm 35 has a right angular form'and'has the outer end thereof connected with one end of a flexible bellows 31 supportedfrom-the wall of the envelope I by an elbow 38: The bellows 31' is sealed at its open end to oneend' of-elbow- 38 and theother end of the elbow is welded-to the envelope As a'means for adjusting the angular position of the tuning disk 33 thereis provided an adjusting screw 39 whichthreadedly'engages a bracket 40 supported from elbow 38. The screw 39 carries a pair of shoulders 4| and .42 which engage the opposite side of an arm 43 secured to the outer end of the bellows so that rotation of the screw 39 is effective to move the bellows and. rotate the tuning disk- 33. While in the arrangement shown, the disk is rotated on flat surfaces of the anode structure 2 it will be understood that a ball bearing structure may be employed in the interest of reducing friction if desired.

The operation of the modification of th invention illustrated in Figs. 4 and 5 is essentially the same as the modification of Fig. 1 with the inductance being the maximum when the disk 33 is rotated so that the openings 3 of the anode structure are entirely unobstructed by the toothlike portions 34. As the disk is rotated to cover more of the openings, the high frequency electromagnetic flux linking the openings is reduced, the inductance is decreased, and the operating frequency of the device is increased.

While I have shown and described particular embodiments of my invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention in its broader aspects, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

VVht I claim as new and desire to secure by Letters Patent of the United States is:

1. A high frequency electric discharge device comprising a sourc of electrons, an anode structure adjacent said electron source and including a plurality of circumferentially disposed anode segments defining inter-segmental spaces between them, each of said spaces consisting of a predominantly inductive and a predominantly capacitive region and being resonant at a frequency determined by the inductance and capacitance of said regions, moveable tuning means mounted adjacent to said anode structure and having a conductive surface in proximity to the inductive regions of said inter-segmental spaces and a further conductive surface in proximity to the capacitive regions of said spaces, and means connected to said tuning means for simultaneously moving one of said conductive surfaces away from said anode structure and the other of said conductive surfaces toward said anode structure whereby the inductance and capacitance of said regions may be simultaneously increased or simultaneously decreased.

2. A high frequency electric discharge device comprising an electron source, an anode structure having a central opening containing said source and further having a plurality of cavities located about nd communicating with said central opening, the bounding surface of each of said cavities defining a predominantly capacitive region and a predominantly inductive region, a pair of concurrently movable conductive members respectively disposed on opposite sides of said anode structure, one of said members extending in close proximity to-the saidcapaciti-ve-regions ofsaid cavities and the other of said'members extending inclose proximity to the inductive regions of said cavities; and means connecte'dto said members for concurrentlymoving one of said members toward said anodestructure and the other of said members away from said structure whereby the inductance and capacitance of said cavities may be simultaneously increased or simultaneously decreased.

3; A high frequency electrical discharge device including a source of electrons, an annular anode structure having a central opening containing said electron source and a plurality cf radially extending anode sections dividing said structureinto a plurality of circumferentially spaced openended cavities communicating with said central opening, the opposed walls of each of said cavities being closer spaced in the region nearer said central opening than the walls of said cavities remote from said central opening, the capacitive component of reactance of said cavities thereby being determined largely by the configuration of the cavities in the region of said central opening and the inductive component of reactance of said cavities being determined largely by the configuration of the cavities in the region remote from said central opening, a pair of generally annular tuning members generally coaxial with said anode structure one located adjacent each end face thereof, one of said members having an outer diameter substantially less than the outer extremities of said cavities whereby it lies in proximity to the capacitance-determining region of said cavities and the other member being of relatively larger diameter whereby it lies in proximity to the inductance-determining region of said cavities, and a positioning mechanism connected to said members for moving said members simultaneously in the same direction whereby one member may move toward said anode structure as the other member moves away from said anode structure whereby the inductive and capacitative components of reactance of said cavities may be simultaneously increased or simultaneously decreased. V

4. A high frequency electric discharge device including an electron source, an annular anode structure having a central opening in communication with said electron source and a plurality of radially extending anode sections dividing said structure into a plurality of circumferentially spaced open-ended cavities, the opposed wall portions of said cavities in the region nearer said central opening being closer spaced than the wall portions of said cavities remote from said central opening, the capacitive component of reactance of said cavities thereby being determined largely by the configuration of the cavities in the region of said central opening and the inductive component of reactance of said cavities thereby being determined largely by the configuration of the cavities in the region remote from said central opening, a pair of tuning members in proximity to said anode structure, means supporting one of said members adjacent the portion of said cavities remote from said central opening, said one of said members thereby being in a position to control the electromagnetic flux through the said portion of said cavities, means supporting the other of said members adjacent the portion of said cavities in the region of said central opening, said other member thereby being in a position to control the capacity between said anode sections, and a positioning mechanism connected to said means for simultaneously moving one of said members toward said anode structure and the other members away from said anode structure whereby the inductive and capacitive components of reactance of said cavities may be simultaneously increased or simultaneously decreased to produce a cumulative change in the operating frequency of said device.

RICHARD B. NELSON.

REFERENCES CITED Number Proc. I.

UNITED STATES PATENTS Name Date Spencer Sept. 24, 1946 Spencer Sept. 24, 1946 Spencer Sept. 24, 1946 Spencer Sept. 24, 1946 Fritz et a1. Apr. 26, 1938 Von Baeyer Jan. 20, 1942 Dallenbach et a1. Aug. 12, 1941 Dallenbach July 25, 1939 OTHER REFERENCES R. 152., March 1944, pages 136-139. 

